1. Field of the Invention
The present invention relates to an image forming apparatus. More specifically, the present invention relates to an image forming apparatus having a feed roller bearing and a print head.
2. Background Information
In conventional practice, various structures for ensuring precision in positioning the print head in relation to a platen roller have been proposed in fax machines and other such image forming apparatuses.
Also, heat transfer printers are known in conventional practice as examples of image forming apparatuses. As shown in the schematic view of FIG. 15a, such heat transfer printer generally includes a chassis 101, a printer head unit 104 pivotably supported by the chassis 101, a platen roller rotatably supported by the chassis 101 opposite the printer head unit 104, a pressing mechanism 107 pivotably supported to the chassis 101, a feed roller 109 rotatably supported by the chassis 101 via bearings, a press roller 110 supported by the chassis 101 opposite the feed roller 109, and a drive gear 108 having a small gear 108a and a large gear 108b for pivoting the pressing mechanism 107.
The print head unit 104 has a support axle 104a, an arm unit 104b, and a print head 104c, as shown in FIG. 15. The print head unit 104 is also mounted on the inner sides of the chassis 101 at the support axle 104a so as to be capable of pivoting, as shown in FIG. 15. Also, as shown in FIG. 15, a helical torsion spring 114 is mounted between the support axle 104a of the print head unit 104 and the chassis 101. This helical torsion spring 114 urges the print head unit 104 in a direction away from the platen roller 105. Also, a bent part 104d that is pressed by the pressing mechanism 107 is formed in the arm unit 104b of the print head unit 104 so as to be bent toward the chassis 101. As shown in FIG. 15, the print head 104c is pressed against the platen roller 105 via the paper 130 and an ink sheet during the printing operation.
Also, the pressing mechanism 107 has two pivoting members 107a each having a toothed section 107d, and a support rod 107c that pivotably supports the pivoting members 107a. Press springs 107e for exerting pressure on the bent part 104d of the press roller 110 are provided to both of the pivoting members 107a. Also, the pivoting members 107a are tightly mounted on the support rod 107c so as to not to be relatively rotatable. The toothed section 107d of one of the pivoting members 107a meshes with the small gear 108a of the drive gear 108, as shown in FIG. 15. In this manner, the drive gear 108 transmits the drive force from a motor to the toothed section 107d of the pivoting member 107a. 
Both ends of the feed roller 109 are supported by the chassis 101 via bearings. Protrusions of a specific height are partially formed by rolling on the surfaces of the feed roller 109.
During the printing operation, the print head 104c of the print head unit 104 is pressed on against the platen roller 105 via the paper 130. As shown in FIG. 15, the bent part 104d of the print head unit 104 is pressed on by the press spring 107e of the pivoting member 107a of the pressing mechanism 107 with an amount of pressure W3. As a result, the print head unit 104 receives an amount of frictional force μW3 in the paper conveying direction (direction of arrow C2 in FIG. 15). The symbol “μ” is the dynamic coefficient of friction. Also, the feed roller 109 receives a reaction force W4 in the opposite direction from the paper conveying direction, as a result of the conveying load of the paper 130 as the feed roller 109 conveys paper 130 during the printing operation.
The conventional heat transfer printer shown in FIG. 15 has drawbacks in that, since the print head unit 104 receives the frictional force μW3 in the paper conveying direction, the unit therefore tends to move in the paper conveying direction (direction of arrow C2 in FIG. 15). As a result, the position of the print head 104c of the print head unit 104 tends to become misaligned in relation to the platen roller 105. Thus, printing precision tends to be compromised. Also, the feed roller 109 tends to be moved in the direction opposite the paper conveying direction together with its bearings due to the reaction force W4 received in the direction opposite the paper conveying direction. Accordingly, precision in feeding of the paper 130 tends to be compromised.
In view of the above, it will be apparent to those skilled in the art from this disclosure that there exists a need for an improved image forming apparatus that overcomes the problems of the conventional art. This invention addresses this need in the art as well as other needs, which will become apparent to those skilled in the art from this disclosure.